Ophthalmic lenses, dioptric formulae for combined cylindrical lenses : the prism-dioptry, and other optical papers (1900)
Prentice, Charles Frederick, b. 1854 · Philadelphia : Keystone · leaf 193
improvement can be obtainedin a similar manner at finite distance, yet it would be exceedingly difficultto accurately place the pin-holes before the pupils of both eyes for readingbinocularly. To obviate this impracticability, while still securing an un-impaired field of fixation, the typoscope, as… … One-half of Actual Size. aperture 4^ by f inches, centrally located, though laterally displaced so asto leave sufficient of the plate, two inches, to be conveniently held betweenthe thumb and fingers, when it is placed upon the book or paper, andwhile it is being slid down over the column in…
Lenses
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